The present invention relates to disc drive storage systems having one or more transducer head assemblies with an air bearing slider that xe2x80x9cfliesxe2x80x9d relative to a rotating disc. and, more particularly, to an overcoat configuration used on such a slider.
Many computer disc drives use discs coated with a magnetizable medium for storage of digital information. The discs are mounted on a spindle motor which causes the discs to spin. Magnetic transducers are supported over the rotating discs, and each transducer writes information to and reads information from the disc surface in any of a plurality of circular, concentric data tracks.
Each transducer head assembly includes a gimbal and an air bearing slider that xe2x80x9cfliesxe2x80x9d relative to the rotating disc and carries the magnetic transducer proximate the rotating disc. An actuator arm moves and positions the slider and the transducer from track to track on the disc surface. The actuator arm includes a load beam for each head gimbal assembly. The load beam provides a preload force which forces the head gimbal assembly toward the disc surface. The gimbal is positioned between the slider and the load beam to provide a resilient support connection for the slider. The gimbal is in point contact with the slider, and provides a point about which the slider can pitch and roll responsive to the wind and while following the topography of the disc.
The sliders include an airbearing surface defined between or around recessed portions. The air bearing surface generally faces the surface of the disc. As the disc rotates, the disc drags air under the slider and along the air bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the air bearing surface, the incident air causes the slider to lift and fly above the disc surface. The shape of the air bearing surface significantly affects the lift and flying characteristics of the slider.
In many sliders, the air bearing surface is provided with a crown from the leading end to the trailing end. The air bearing surface may also be formed with a cross-curve from one side to the other. The crown and the cross-curve can be formed as the intersection of two cylindrical profiles, or as a spherical profile to the air bearing surface.
The xe2x80x9cflying heightxe2x80x9d of the slider or clearance at the transducer is an important parameter to the disc drive performance. It is desired to minimize the flying height, and to minimize variations in flying height. A consistent, minimal flying height results in increase areal density of recording and a reduced chance of data error. However, as flying height is continually decreased, the tribological interaction between the disc and the slider becomes more critical toward preventing crashes.
While the disc drive is not operating, rotation of the discs is typically stopped. Without the incident wind, the slider is parked in contact with the disc on a landing zone. Interaction between the slider and disk during parking, start-up and slow down is also important to disc drive performance. During start-up, the static friction or xe2x80x9cstictionxe2x80x9d between the slider and the disc must not be so great as to exceed to power of the spindle motor. Wear on the slider or the disc during start-up and slow-down should be minimized or directed at non-critical features of the slider and disc.
In many sliders, the air bearing surface includes a pair of side rails each positioned along side edges about a recessed central cavity. The side rail closest to the disc hub is called the xe2x80x9cinner railxe2x80x9d and the side rail closest to the disc rim is called the xe2x80x9couter railxe2x80x9d. A leading taper may be used to pressurize the air as the air is dragged by the disc under the air bearing surface. The rails may extend from the taper to the trailing edge. A self-loading, negative (or subambient) pressure air bearing slider (NPAB) includes a cross rail which extends between the side rails and is positioned near the slider""s leading edge. The cross rail can also be referred to as a xe2x80x9cthroatxe2x80x9d or a xe2x80x9cdamxe2x80x9d. The cross rail impedes incident air from the trailing central cavity. The air passing beneath the slider expands in the cavity, resulting in a decrease in pressure to subambient. The subambient pressure cavity may recessed from one-tenth to ten microns from the air bearing surface. In some slider designs, the air bearing surface includes a central pad toward the trailing edge of the central cavity. In other designs, central rails are included between the side rails. The transducer is typically mounted at the trailing edge of the slider, either on one or both of the side rails or on the central pad or central rail. If the transducer is mounted on a central pad or central rail, the side rails may be truncated prior to the trailing edge.
The disc tangential velocity is greater at outer tracks than at inner tracks, resulting in differing wind speeds dependent upon where the slider is positioned over the disc. Many disc drives utilize rotary actuators which move the slider from track to track over a rotary arc. In rotary actuated drives, the slider changes xe2x80x9cskew anglexe2x80x9d from inner tracks to outer tracks. Differing wind speeds and differing skew angles commonly contribute to variations in flying height.
Manufacture of the slider includes numerous fabrication steps, which are typically carried out in batch form to a plurality of sliders to increase efficiency. A typical fabrication process begins with a wafer of substrate material of a thickness which generally corresponds to the desired lengths of the sliders. An array of transducers are photolithographically fabricated on the wafer as known in the art. The wafer is then be cut into slider bars, with each slider bar including a line of sliders. The cut surfaces provide the top faces and bottom (i.e., air bearing) faces of the sliders. The air bearing faces are lapped to a smooth and flat surface suitable for application of milling pattern masks, and the leading edge of the slider bar may be lapped at an angle to provide the taper. Any crown or cross-curve may also be lapped into the sliders. The slider bars are oriented bottom-face-up (i.e., air bearing face exposed, transducers on a side face) and reassembled on a processing substrate to form a second array. Overcoat material is deposited onto the air bearing face and exposed pole tip of the transducer. The second array is photolithographically processed, removing material to form the cavity and define the rails and any crossbar and/or central pad. For instance, ion milling, chemical etching, or Reactive Ion Etching (RIE) may be used for material removal. Additionally lapping or reflat processes may further smooth the air bearing surface. The slider bars are cut to form individual sliders and removed from the processing substrate, and the individual sliders are attached into the head gimbal assemblies.
Each of the fabrication steps is not entirely controllable. Each additional fabrication step increases the time required for fabrication, increases slider fabrication cost, reduces slider yield by stacking up additional tolerances, and complicates slider design and modeling. At the same time as a highly efficient fabrication process is desired, the resultant product must provide the minimal flying height for increased areal density, and also maximal robustness against crashes.
The present invention is an air bearing slider for a disc drive, having an overcoat localized on the air bearing surface to provide a continuous covering over a leading portion of the air bearing surface. The overcoat terminates in a trailing cut-off line, and a trailing portion of the air bearing surface is not covered by overcoat. By removing the overcoat from the trailing portion of the air bearing surface, the flying height of the transducer is minimized because the overcoat does not take up any of the head-disc separation budget. By having the overcoat in a continuous covering over the leading portion of the air bearing surface, the entirety of the air bearing surface that ordinarily contacts the recording medium in contact/start/stop is protected by a uniform flat overcoat layer. In one aspect of the invention, the overcoat also covers the pole tips of the transducer at a pole tip recession from the air bearing surface. In another aspect of the invention, the trailing cut-off line is disposed at an angle to expose the trailing corners of the air bearing surface, such that all of the overcoat is elevated above the lowermost portion of the air bearing surface through pitch and roll angles of flying at inner and outer radii.